Airbag modules currently used in automobiles comprise a reaction canister containing an inflator for rapid generation of gas to inflate an airbag. The inflator is activated upon rapid deceleration of the automobile as in a collision. Gas issues from the inflator into the reaction canister and thence flows into the airbag which is folded and stored inside an airbag container which is fastened to or is a part of the reaction canister. Generally the reaction canister has a bottom, sidewalls and end walls. The side and end walls form a trough-shaped airbag container for storing the folded airbag. The airbag has an open mouth connected to the reaction canister for flow of gas from the reaction canister into the airbag to inflate the airbag.
The top of the airbag container is an open end from which the airbag will be deployed as it is inflated. The canister is installed in a vehicle with the open top of the airbag container just below the instrument panel. This open top of the airbag container is covered by a face panel of a deployment door which is fastened to the reaction canister either directly or through other members of the airbag module. The face panel of the deployment door is designed for placement at an opening which is provided on the vehicle instrument panel for deployment of the airbag through that opening. Typically the face panel is made from the same material as, or a material that matches the instrument panel, usually a flexible molded plastic.
The airbag module is installed in the vehicle by attaching the reaction canister to structural support members in the vehicle beneath the instrument panel. The module is positioned there with the open top of the airbag container at an opening that is provided in the instrument panel. The deployment door is fastened to the reaction canister by connections near the edges of the airbag container at its open top.
The deployment door is held shut by breakable means such as a breakable tear seam on the face panel of the deployment door. By the force of the airbag pressing against the deployment door as the airbag begins to be inflated, the breakable means will be broken or torn and the door will open to give way for deployment of the airbag from its container and through the opening in the instrument panel. As inflation proceeds, the deployed airbag will expand into the passenger compartment of the vehicle.
The deployment door not only covers the open top of the airbag container or reaction canister to hold the folded airbag inside the container or canister but it also covers an opening in the instrument panel which is provided for deployment of the airbag. The face panel of the deployment door is a visible part on the outer surface of the instrument panel and it is usually designed to match the decor of the instrument panel.
An airbag module must be installed with secure fastening of its several elements to the reaction canister. The fastenings must be strong enough to resist disintegration of the module under sudden forces that are exerted as the inflator is actuated and the airbag is inflated and deployed. The reaction canister absorbs reaction forces from the several elements of the module and transmits those forces from the module to the vehicle through structural members to which the reaction canister is fastened in the vehicle. It is important that the deployment door remains attached to the airbag module when the door is forced open by impact of the deploying airbag. If the deployment door were attached only to the instrument panel, reaction to the force required to open the deployment door would be transmitted only to the instrument panel, which might cause the deployment door to break loose and be hurled into the passenger compartment; or such forces might damage the instrument panel.
A frequent problem in the installation of airbag modules with conventional deployment doors is poor fit and finish between the instrument panel and the deployment door. When the airbag module is installed with the deployment door fixed immovably to the reaction canister, it is often difficult to obtain the desired accuracy of fit and finish between the face panel of the deployment door and the instrument panel. The airbag module is installed in the vehicle by fastening the reaction canister to structural members of the vehicle under the instrument panel. There may be an accumulation of several tolerance variations between the vehicle members to which the reaction canister is fastened and the instrument panel surface, which may cause inaccurate fit and finish at the instrument panel.